"12 nm" is just another iteration of the 20 nm node. Ten years ago, everyone would have been damn embarassed by calling it 12 nm, which isn't even an ITRS node name.
The only chance this is really good and not merely a larger Pascal is another Kepler -> Maxwell surprise, but sudden improvements are less and less likely as time goes by (though Nvidia have been developing the Volta architecture for quite a longe time, so...).
Still I also expect it to release by September or so at latest, unless Nvidia has some insider knowledge the next node shrink is going to take longer than expected, and thus are stretching over time what they have. It's not like they delay products because they are comfortable on the market or their stuff still sells, it would be surprising and disappointing if they suddenly became another Intel (as people think Intel does, at least).
